1. Field of the Invention
The present invention relates to a diffusion bonding target assembly of a high-purity cobalt target and copper alloy backing plate which does not generate warping or peeling upon diffusion bonding, and the manufacturing method thereof.
2. Description of the Related Art
Conventionally, when performing magnetron sputtering to a ferromagnetic target such as cobalt upon disposing a magnet to the back side of such target, it is difficult to generate a magnetic field on the target surface since the magnetic field will be blocked within the target. In other words, due to the magnetic field characteristic to cobalt, which is a ferromagnetic, the plasma density will not increase and the ionization efficiency of argon will decrease, thereby resulting in low sputtering efficiency.
Thus, when employing a ferromagnetic target such as cobalt, measures of merely thinning the target thickness were taken in order to leak the magnetic field.
Generally, with the conventional bonding of a target and backing plate, a low melting bonding material such as indium was used.
Nevertheless, since this type of bonding material (brazing filler material) such as indium is easily affected by heat, there is a problem in that it is not suitable for high power sputtering. In view of the above, diffusion bonding that does not use brazing filler material has been proposed.
Numerous actual performances with titanium and aluminum have been achieved in this diffusion bonding, and there is an advantage with diffusion bonding items in that aluminum or aluminum alloy, which is inferior in thermal conductivity in comparison to copper, may be used as the backing plate since such items do not use a brazing filler material. Moreover, since the specific gravity of aluminum is approximately ⅓ of that of copper, there is a benefit in that the target may be made lighter, and the handling will improve.
Nevertheless, with the combination of cobalt and aluminum or aluminum alloy, since the difference in the coefficient of thermal expansion is so large in comparison to titanium or aluminum, there is a possibility in that deformation may occur from the difference in coefficient of thermal expansion due to the bimetal effect when the temperature becomes too high.
In recent years, a method for performing even deposition is employed by ionizing sputtering particles with further high power sputtering and providing strong kinetic energy to the substrate. As a result, there are cases where a target to which is bonded a backing plate deforms due to the hydraulic pressure of the thermal influence and cooling medium during sputtering, and water may leak thereby.
Recently, the target itself is being enlarged pursuant to the enlargement of the aperture of the wafer, and problems such as the peeling of the bonding boundary face and deformation of the backing plate are becoming even more serious.
As an example, a target assembly was prepared by diffusion bonding an aluminum alloy (A5052) backing plate to a 350 mm cobalt target (purity of 5N) having a thickness of 3 mm in a vacuum, at 450xc2x0 C. with a bearing of 15 kgf/mm2, and retained for 5 hours. Water leaked when this was used for the sputtering at a sputtering power of 30 KW. The cause of this was due to the center portion deforming to a convex shape and the diffusion bonding portion partially peeling off, and the aluminum alloy of the backing plate becoming deformed thereby.
In light of the foregoing circumstances, conventional diffusion bonding and backing plates are not able to prevent the generation of warps and peeling upon diffusion bonding, and the discovery of a new material and diffusion method was in need.
In view of the above, provided is a diffusion bonding target assembly of a high-purity cobalt target and a copper alloy backing plate capable of effectively sputtering a high purity cobalt ferromagnetic target and which does not generate warping or peeling upon diffusion bonding even under severe conditions such as bonding with the backing plate and high power sputtering, and the manufacturing method thereof.
As a result of intense study, the present inventors have discovered that warping and peeling may be effectively prevented by suitably selecting a material to be intervened upon diffusion bonding with a strong backing plate.
Based on the foregoing discovery, the present invention provides: 1) a diffusion bonding target assembly of a high purity cobalt target and a copper chrome alloy or copper zinc backing plate, wherein aluminum or aluminum alloy having a thickness of 2 mm or more is used as the insert material upon diffusion bonding the target assembly, and the warp after bonding is 1.5 mm or less; and 2) a diffusion bonding target assembly of a high purity cobalt target and a copper chrome alloy or copper zinc backing plate, wherein aluminum or aluminum alloy having a thickness of 2 mm or more is used as the insert material upon diffusion bonding a high purity cobalt target and a copper chrome alloy or copper zinc alloy backing plate in a vacuum at a temperature of 200xc2x0 C. to 450xc2x0 C. under a pressure condition of 1 to 20 kg/mm2, and the warp after bonding is 1.5 mm or less.